Plant parasitic nematodes cause serious economic damage to many agricultural crops around the world. The nematodes in this group are microscopic worms and in general are obligate parasites of plants. They feed mostly on the roots of host plants; however, several genera are known to parasitize above-ground parts including stems, leaves and flowers as well. Almost all the plant species of economic importance are susceptible to infection by some species of nematodes. For example, root knot nematodes (RKN), (Meloidogyne spp.) are capable of parasitizing more than 3,000 species of crop plants.
The symptoms due to parasitic nematode injury vary widely depending on the plant host, the nematode species, the age of the plant, geographical location and climatic and external environmental conditions. In general, an overall patchy appearance of crop plants in a field is considered to be indicative of nematode infestation. More specifically, nematode injury can manifest itself, for example, as galling of the roots (abnormal swelling in the tissue due to rapid multiplication of cells in the cortical region) caused by species of root knot (Meloidogyne spp.) and cyst (Heterodera spp.). Nematodes can also be vectors of plant viruses and are also known to induce disease complexes, predisposing plants to infection by other plant pathogenic fungi and bacteria.
Chemical nematicides, either soil fumigants or non-fumigants, have been in use for many years and are among the few feasible options for countering nematodes. At present, repeated applications of synthetic chemicals to the field are required prior to planting the crop. These chemicals are extremely toxic to non-target organisms besides nematodes and many of them may pose serious threats to the environment. Because of these downfalls, there is a need for effective nematicides with low toxicity.
Plant essential oils, which do not present any known risk to humans or to the environment, are qualified for an exemption as minimum risk pesticides and are listed in 40 C.F.R. §152.25 (b). However, high volatility, phytotoxicity and low water solubility of some oils have limited their use in crop protection.
The nematicidal activity of cinnamaldehyde is known. For example, ProGuard® 30% Cinnamaldehyde Plowable Insecticide, Miticide and Fungicide (U.S. Pat. Nos. 6,750,256 B1 and 6,251,951 B1) demonstrates that cinnamaldehyde has nematicidal activity in the presence of a 2% Tween 80 and 6% NaHCO3. However, a disadvantage of this commercial product is that it contains the chemical preservative o-phenylphenol. Further, cinnamaldehyde may result in plant phytotoxicity especially when used at rates high enough to provide nematode protection (500 ppm and above).
Garlic extract may be known to control nematodes, however, the cost of garlic extract is too prohibitive to be a practical solution to nematode infestation of a field. Further, garlic extract formulations are often aqueous and the stability of the active components in aqueous preparations is questionable.
U.S. Pat. No. 4,978,686 (“the '686 patent”) suggests a composition comprising cinnamaldehyde, an antioxidant, an emulsifier, and water. However, the '686 patent does not teach or suggest the use of cinnamaldehyde with ailicin formulated together to provide superior nematicdial activity.
Accordingly, there is a need to develop a safe, easy-to-use, cost-effective delivery system, so as to improve the biological effectiveness of plant essential oils/plant extracts, for agricultural applications. There is especially need for an effective and environmentally safe nematicide formulation.